Antimicrobial Use and Stewardship

CDFA-AUS  •  1220 N Street, Sacramento, CA 95814  •  916-576-0300

Resources & Outreach

The AUS program provides resources for all stakeholders, including veterinarians and producers, about the effort in California to reduce antimicrobial resistance in livestock. Below please find outreach and educational materials, best management practices and guidance documents, programmatic reports, and other publications produced or supported by the AUS program. Information on AUS presentations and events, past and upcoming, is also provided. Additionally, other resources related to antimicrobial resistance education and research are listed.

Frequently Asked Questions:

Answers to frequently asked questions regarding the AUS program.

English  |  Spanish (Español: Preguntas Frequentes)

Requirements for Prescription Antibiotics:

Existing requirements for veterinary prescriptions, options for filling prescriptions, and establishing a valid veterinarian-client-patient relationship (VCPR).

Veterinarian    |  Producer  |  Spanish (Español: Requisitos para Antibióticos Recetados)

AUS Annual Reports: Description and highlights of program activities reported for each fiscal year. Attached appendices provide more detailed information for a selection of AUS' studies and projects.

Veterinary Feed Directive (VFD) Summary Reports: Annual summaries of manufacturing and distribution data for California medicated feed containing a VFD drug or combination VFD drugs, by VFD order written by a licensed veterinarian.

AUS Report to the Legislature: The AUS Report to the Legislature, published in 2019, fulfills the mandate in FAC 14405 (d) by providing the results of the program’s outreach activities and monitoring efforts during its first years of implementation.

AUS Report to the Legislature  |  News Release

AUS Strategic Plans: AUS publishes its Strategic Plans as appropriate to update stakeholders on programmatic goals and plans for implementation.

2018 Strategic Plan

CAHFS Antibiogram Development Process : These slides outline the steps involved in creating Minimum Inhibitory Concentration (MIC) data and how the MIC data is used to develop antibiograms based on the process currently utilized by the California Animal Health and Food Safety Laboratory (CAHFS).
California Livestock Antibiograms: A User Guide : This document serves as a guide for veterinarians on how to interpret and apply antibiograms in clinical practice. Antibiograms are a clinical tool that can help optimize veterinary approaches to antimicrobial therapy, specific to a particular bacteria and drug combination. Please note: All CAHFS antibiograms are for advisement only and are intended to be used by veterinarians.

CDFA AUS – Best Management Practices (BMPs) // Vaccine Handling Guidelines: Five infographics providing foundational knowledge of proper vaccine handling to ensure an effective vaccination program.

CDFA AUS – Best Management Practices (BMPs) // Vaccine Handling Guidelines – Resources for Veterinarians: These veterinary considerations offer a more in-depth instruction on the nuances of creating an effective vaccination program, along with additional scientific resources.

These cow calf guidelines provide direction for producers and veterinarians to assist with the detection, prevention and management of the top three diseases that can lead to antibiotic use in cow calf operations: pinkeye, scours and bovine respiratory disease.

The documents titled Strategies for Management are infographic documents designed for producers. The documents titled Practical Guide for Veterinarians are to be used by veterinarians in addition to the infographic guidelines.

Bovine Respiratory Disease

Antimicrobial Stewardship Principles: Please visit the AUS Antimicrobial Stewardship page.

Guidelines for Judicious Use of Antimicrobials: These guidelines are intended to support decision-making surrounding responsible antibiotic use, under the guidance of a veterinarian in compliance with state and federal laws.

Veterinarian–Client–Patient Relationship (VCPR) Resources: Establishing a veterinarian–client–patient relationship (VCPR) is an essential first step in the development of an Antimicrobial Stewardship Plan.

Antimicrobial Selection: Considerations for Veterinarians : This guide provides an overview of concepts to consider when using antimicrobial susceptibility test data to guide clinical decisions.

These cattle-specific fly identification, monitoring, and tracking resources support producers in identification/monitoring of common cattle fly pests, as well as provide the framework for development and evaluation of on-farm pest management plans. The Fly Identification, Monitoring, and Tracking Resource specifically provides a comprehensive overview of cattle fly pest management, with species-specific information and infographics, monitoring guidelines, and resources for pest management strategies.

2017 Cow Calf Survey: Summary findings from AUS’ 2017 survey of antibiotic use and stewardship on California’s cow calf operations.

2017 Cow Calf Survey  |  Español: Encuesta de Terneros 2017

2018 Commercial Sheep Survey: Summary findings from AUS’ 2018 survey of antibiotic use and stewardship on California’s commercial sheep operations.

2018 Commercial Sheep Survey  |  Español: Encuesta de Ovejas Comerciales 2018

Partnering for Dairy Antimicrobial Stewardship: A Conference for Farmers and Veterinarians in the West (July 2020)

Recordings: July 8  |  July 15  |  July 22  |  July 29

Upcoming: Visit here for information on upcoming AUS presentations, events, and opportunities to get involved with the program.

Veterinary Feed Directive (VFD) Resources: Resources related to VFDs and VFD orders. For more information on VFDs, please visit the CDFA FFLDRS Livestock Drug Program page.

Confidentiality in Data Reporting: Brochure with information on AUS’ approach to confidentiality in data reporting.

AUS Surveys & Studies Resources: Materials addressing the who, what, why, and how the AUS program is collecting information on California animal agriculture and what you can do to help. For more information on AUS Surveys & Studies, please visit the Surveys & Studies page.

Antimicrobial Stewardship During COVID-19 Pandemic: COVID-19 has brought numerous challenges to the animal production industry. This infographic lists considerations for the continuation of antimicrobial stewardship in livestock during the COVID-19 pandemic.

In addition to materials, events, and research produced by the AUS team, the AUS program provides funding and support for a number of studies, projects, publications, and other resources led by external partners. Below find information on work produced with AUS funding and/or collaborative support.

Please Note: The New flag indicates publications new to this list, not necessarily chronological in time for work performed or publication date. To facilitate searching for subjects of interest, keywords have been provided for each publication.

Abdelfattah EM, Ekong PS, Okello E, Chamchoy T, Karle BM, Black RA, Sheedy D, ElAshmawy WR, Williams DR, Califano D, Tovar LF. Epidemiology of antimicrobial resistance (AMR) on California dairies: descriptive and cluster analyses of AMR phenotype of fecal commensal bacteria isolated from adult cows. PeerJ. 2021;9.

This study describes the occurrence of antibiotic resistance in commensal Escherichia coli and Enterococcus/ Streptococcus spp. isolated from fecal samples of dairy cows and assesses the variation in antibiotic resistance profiles across regions and seasons following the implementation of the Food and Agricultural Code (FAC) Sections 14400 - 14408 (formerly known as Senate Bill, SB 27) in California.

Keywords: antimicrobial resistance; dairy cattle; Escherichia coli, Enterococcus spp; multidrug resistance, phenotype; California; region; season; cohort study

Abdelfattah EM, Ekong PS, Okello E, Williams DR, Karle BM, Rowe JD, Marshall ES, Lehenbauer TW, Aly SS. 2019 Survey of Antimicrobial Drug Use and Stewardship Practices in Adult Cows on California Dairies: Post Senate Bill 27. Microorganisms. 2021 Jul;9(7):1507.507.

In this project, surveys were sent out to 1282 California dairies in both 2018 and 2019 to determine and evaluate changes in antibiotic use, health management, and antibiotic drug stewardship practices of adult cows on California dairies following the initiation of implementation of California Food and Agriculture Code 14400 - 14408 (formerly SB 27).

Keywords: antimicrobial drug resistance; antimicrobial stewardship; California; dairy cattle; judicious use; survey

Basbas C, Byrne BA, Chigerwe M, Escobar ED, Hodzic E, Pires AF, Pereira RV. Detection of Cephalosporin and Fluoroquinolone Resistance Genes via Novel Multiplex qPCR in Fecal Salmonella Isolates From Northern Californian Dairy Cattle, 2002 - 2016. Frontiers in Microbiology. 2021;12.

In this study, Salmonella isolates obtained from dairy cattle were screened for beta-lactam resistance genes, focusing on genes linked to resistance to cephalosporin drugs, and quinolone resistance genes. Testing included whole genome studies focusing on isolates resistant to quinolones to identify potential chromosomal mutations leading to resistance to quinolone drugs. Temporal distribution of genetic elements was evaluated for links to antibiotic resistance, as well as potential trends or factors that could have influenced changes in their prevalence.

Keywords: fluoroquinolone; cephalosporin; qPCR; antimicrobial resistance genes; Salmonella

New Chen, S.-Y.; Negri Bernardino, P.; Fausak, E.; Van Noord, M.; Maier, G. (2022) Scoping Review on Risk Factors and Methods for the Prevention of Bovine Respiratory Disease Applicable to Cow-Calf Operations. Animals, 12, 334.

This scoping review summarizes the English scientific literature on articles about risk factors for the disease as well as ways to prevent bovine respiratory disease (BRD) that are applicable to cow-calf operations. Numerous management and animal factors have been identified as increasing the risk for BRD. Vaccinations, metaphylactic use of antibiotics, and feed supplements are areas of research into the prevention of BRD. Genetics have also been explored to determine the heritability of BRD resistance. While vaccinations and metaphylactic use of antibiotics have been evaluated in multiple systematic reviews and meta-analyses, these types of summaries are missing for commonly studied feed supplements, such as yeast and trace minerals, and the use of nitric oxide releasing substance to prevent BRD.

Keywords: bovine respiratory disease, prevention, risk factors, antimicrobial stewardship, shipping fever

Depenbrock S, Aly S, Wenz J, Williams D, ElAshmawy W, Clothier K, Fritz H, McArthur G, Heller M, Chigerwe M. In-vitro antibiotic resistance phenotypes of respiratory and enteric bacterial isolates from weaned dairy heifers in California. PLoS One. 2021 Nov 24;16(11):e0260292. doi: 10.1371/journal.pone.0260292. PMID: 34818352; PMCID: PMC8612539.

This study aimed to provide data from weaned dairy heifers regarding antimicrobial resistance in bovine respiratory isolates and identify relationships between respiratory and enteric antimicrobial drug susceptibility. A cross-sectional study was performed between June 2019 and February 2020 on six calf rearing facilities in California. Deep nasopharyngeal and rectal swabs were collected from 341 weaned heifers and submitted for selective bacterial culture and antimicrobial susceptibility testing against 19 antimicrobial drugs. Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni were selectively isolated from respiratory samples; Escherichia coli and Enterococcus spp. were selectively isolated from rectal swabs. Antimicrobial resistance (AMR), including multidrug resistance, in respiratory isolates appears to be widespread in weaned dairy heifers; enteric bacterial susceptibility appears to have limited direct association with respiratory isolate AMR classification.

Keywords: antimicrobial resistance; bovine; dairy; heifers; MIC; respiratory; Mannheimia haemolytica; Pastuerella multocida; Entrerococcus; Escherichia coli; bacterial pathogens; cattle; enteric; California; BRD

Ekong PS, Abdelfattah EM, Okello E, Williams DR, Lehenbauer TW, Karle BM, Rowe JD, Aly SS. 2018 Survey of factors associated with antimicrobial drug use and stewardship practices in adult cows on conventional California dairies: immediate post-Senate Bill 27 impact. PeerJ. 2021 Jul 13;9:e11596.

This project examined good antibiotic drug stewardship practices on conventional dairies in California using survey data from 2018 that was previously described in another publication. The authors applied machine learning to model the associations between management practices and seven outcome variables relating to antibiotic use and stewardship.

Keywords: California dairy industry; antimicrobial drug use; antimicrobial stewardship; judicious use of antibiotics; risk factors; logistic regression; machine learning; decision tree; random forest; gradient boosting

Ekong PS, Abdelfattah EM, Okello E, Williams DR, Lehenbauer TW, Karle BM, Rowe JD, Marshall ES, Aly SS. 2018 Survey of antimicrobial drug use and stewardship practices in adult cows on California dairies: post-Senate Bill 27. PeerJ. 2021 Jul 13;9:e11515.

In this project, surveys were sent out to 1282 California dairies in both 2018 and 2019 to determine and evaluate changes in antibiotic use, health management, and antibiotic drug stewardship practices of adult cows on California dairies following the initiation of implementation of California Food and Agriculture Code 14400 - 14408 (formerly SB 27).

Keywords: California dairy industry survey; antimicrobial resistance; antimicrobial stewardship; antimicrobial drugs (AMD); judicious use of AMD

Hollister, Julia. “Dry Cow Therapy: A Prescription for Success.” Progressive Dairy, 26 Aug. 2020,

An article published in the publication Progressive Dairy promoting an AUS funded study that explores the use of Selective Dry Cow Therapy in dairy herds and the opportunity to reduce the use of antibiotics in dairy production systems, which may also be an economic opportunity for dairy farmers.

Hommels NM, Ferreira FC, van den Borne BH, Hogeveen HT. Antibiotic use and potential economic impact of implementing selective dry cow therapy in large U.S. dairies. Journal of Dairy Science. 2021 Apr 30.

In this study, the objectives were to evaluate the economic feasibility of implementing selective dry cow therapy (SDCT) in large U.S. dairy herds and to estimate the potential reduction in antibiotic use around the dry period if SDCT management is adopted. Cow-level data were obtained from the Dairy Herd Improvement Association and individual dairy herds in California. Logistic regression models were used to predict the incidence risk of subclinical and clinical mastitis in the subsequent lactation for 96 last test-day somatic cell score categories. This study showed that it is economically feasible on some farms to reduce antibiotic use associated with dry cow therapy in large U.S. dairy herds. This contributes to the efforts of reducing antibiotic use worldwide.

Keywords: selective dry cow therapy; antibiotic use; economics; optimization

New Maier, G, Breitenbuecher J, Gomez JP, Samah F, Fausak E, Van Noord M (2022). Vaccination for the Prevention of Neonatal Calf Diarrhea in Cow-Calf Operations: A Scoping Review. Veterinary and Animal Science, Volume 15: 100238, ISSN 2451-943X,

Neonatal calf diarrhea (NCD), also known as scours, is an important disease of preweaned calves that affects the production and welfare of beef herds. While hygiene and nutrition are important in reducing the incidence of NCD, vaccination of dams or calves is often employed for the prevention of NCD. This scoping review summarizes the available peer-reviewed scientific English literature on vaccination of dams or calves for the prevention of NCD over the past decades. In the 113 articles included in the review, vaccines tested targeted the pathogens E. coli (n = 43), bovine rotavirus (BRV, n = 38), Salmonella (n = 29), bovine coronavirus (BCV, n = 14), bovine viral diarrhea virus (n= 7), and other pathogens (n = 8). Field trials for commercial vaccines have been published for the most important pathogens, and results on efficacy are variable for such vaccines targeting BRV, BCV, and E. coli. Meta-analyses exploring efficacy of these vaccines would be helpful to practitioners and producers. No field studies on commercial products have shown efficacy for Salmonella vaccines, so that a meta-analysis would unlikely come to a different conclusion. Further research is needed on vaccines for protozoal pathogens like Cryptosporidium parvum as well as on the importance of several emerging enteric viruses in calves.

Keywords: calf scours, diarrhea, enteritis, vaccine

Michael A, Kelman T, Pitesky M. Overview of quantitative methodologies to understand antimicrobial resistance via minimum inhibitory concentration. Animals. 2020 Aug;10(8):1405.

Minimum Inhibitory Concentration (MIC) testing is a common method of measuring the susceptibility of bacteria to antibiotic drugs. Several quantitative techniques exist for analyzing MIC data, but the application of these methods is not consistent across studies and no guidelines exist for how to choose the most appropriate method. The purpose of this paper is to outline important considerations for selecting the appropriate analytic method to use with MIC data based on the purpose and context of the study.

Keywords: MIC; AMR; mixed effect models; logistic regression; cumulative logistic regression; accelerated failure time-frailty models; mixture models

New Morgan, B L, Depenbrock, S, Martinez-Lopez, B. Identifying Associations in Minimum Inhibitory Concentration Values of Escherichia coli Samples Obtained from Weaned Dairy Heifers in California using Bayesian Network Analysis. (2022) Frontiers in Veterinary Science, Vol. 9, ISSN: 2297-1769.

Many antimicrobial resistance studies in both human and veterinary medicine use traditional statistical methods that consider one bacteria and one antibiotic match at a time. A more robust analysis of antimicrobial resistance patterns in groups of animals is needed to improve on traditional methods examining antibiotic resistance profiles, or the associations between the patterns of resistance or reduced susceptibility for all isolates in an investigation. The use of Bayesian network analysis can identify associations between distributions; this investigation seeks to add to the growing body of antimicrobial resistance pattern research by using Bayesian networks to identify relationships between susceptibility patterns in Escherichia coli isolates obtained from weaned dairy heifers in California.

Keywords: bovine, Bayesian Network Analysis, minimum inhibitory concentration, antibiotics, antimicrobial resistance

Okello E, Williams DR, ElAshmawy WR, Adams J, Pereira RV, Lehenbauer TW, Aly SS. Survey on antimicrobial drug use practices in California preweaned dairy calves. Frontiers in Veterinary Science. 2021;8.

This survey allows immediate assessment of the impact of VFD final rule implementation and provides baseline data for future evaluation of the impact of VFD as well as SB 27 regulatory changes. The knowledge gained from this study is a valuable resource that could guide future recommendations for best health management practices and promote antibiotic stewardship efforts.

Keywords: antimicrobial drug use; veterinary feed directive; perception; preweaned dairy calves; California Senate Bill 27

Sheedy DB, Okello E, Williams DR, Precht K, Cella E, Lehenbauer TW, Aly SS. Effect of Antimicrobial Treatment on the Dynamics of Ceftiofur Resistance in Enterobacteriaceae from Adult California Dairy Cows. Microorganisms. 2021 Apr;9(4):828.

This study investigates the time to peak population and time to return to pre-treatment population of phenotypically ceftiofur-resistant enteric commensal bacteria in response to systemic antibiotic treatment, in commercial dairy cows during the first 60 days of lactation, on two California dairies each across two seasons.

Keywords: antimicrobial resistance; ceftiofur; medically important antimicrobial drugs; dairy; minimum inhibitory concentration

Sheedy DB, Samah FE, Garzon A, Fausak E, Van Noord M, Angelos JA, Maier GU. Non-antimicrobial approaches for the prevention or treatment of infectious bovine keratoconjunctivitis in cattle applicable to cow-calf operations: A scoping review. Animal. 2021 Jun 1;15(6):100245.

Findings of the AUS 2017 Cow Calf Survey of California producers showed that pinkeye was one of the top three diseases of concern in this livestock population. In response, AUS funded a study to further explore options for producers to reduce the burden of this disease. In this scoping review, various non-antibiotic options for management of pinkeye were explored, resulting in the determination that further research is needed on the efficacy of fly control, and on non-antibiotic treatment options such as topical disinfectants or immune stimulants. The continued search for a viable vaccine, as well as identifying genetic markers associated with traits that confer resistance to the disease, are also needed.

Keywords: breed susceptibility; fly control; Moraxella bovis; pinkeye; vaccine

FARM Everyday Biosecurity Reference Manual: Farmers Assuring Responsible Management (FARM) has released a manual that includes management practices designed to protect cattle and people from disease exposure, which can in turn reduce antimicrobial use. The Everyday Biosecurity Manual provides you with the steps to get started and build additional protections for your cattle.

FARM Everyday Biosecurity Reference Manual